The proposed studies represent our continued efforts to characterize bile salt sulfotransferase (BSS), the enzyme systems responsible for the sulfation of bile duct salts. Monohydroxy bile salts such as lithocholic acid and its conjugates cause bile injury, periportal fibrosis and liver cell necrosis. Sulfation of these compounds enhances their elimination, and may represent the major mechanism for removal of these hepatotoxins. We have recently identified at least two forms of BSS in rat liver. We propose to (1) purify and characterize each BSS isozyme. (2) Study the changes in each isozyme: a) during development, b) by gonadal hormones and nongonadal hormones by bile acid substrates and d) by chemical induction. Enzyme purification will involve DEAE-Sephadex column chromatography, bile acid Sepharose and PAP-Agarose (adenosine-3 feet, 5 feet-diphosphate-hexane-agarose) affinity chromatographies and Chromatofocusing. The purified enzymes will be characterized by their substrate specificities, molecular structures, kinetic parameters and immunological properties. Similarities and differences of BSS isozymes and their physiological functions will be ascertained. We will also investigate the isozyme patterns during fetal life and during postnatal development to puberty. Since BSS has been shown to be under both hormonal and drug control, experiments will be carried out to examine the effects of these agents on BSS activity. The information acquired from these studies will help in understanding the mechanisms involved in the detoxification and elimination of hepatotoxic monohydroxy bile acids, and will provide a basis for future studies of bile salt sulfation in man.